The aims of the program are to study the mechanism of contraction in cardia muscle. The focus is on fundamental properties, i.e., on the manner in whic force is generated and regulated. Several specific issues are to be investigated using complementary methodologies. In Project I, several ultrastructural features will be examined with optical microscopy and electron microscopy of quickly frozen specimens. In Project II, the molecular events attendant with Ca activation will be studied using a fluorescent probe, radioactively labelled tracers, and the electron microprobe. In Project III the mechanism underlying the influence of sarcomere length on myofilament sensitivity to calcium will be studied using mechanical and microprobe methods. Project IV will employ unique peptides to inhibit actomyosin interaction and thereby allow study o interaction between actin and myosin.